Improved logic for determining visiblility of activities in the home stack

- No other activity in the home stack should be visible behind the home
activity. Home activities is usually a translucent activity with the
wallpaper behind them. However, when they don't have the wallpaper
behind them, we want to show activities in the next application stack
behind them vs. another activity in the home stack like recents.

- We don't want any other activities in the home stack visible if the
recents activity is going to be returning to an application activity
type. We do this to preserve the visible order the user used to get
into the recents activity. The recents activity is normally
translucent and if it doesn't have the wallpaper behind it the next
activity in the home stack shouldn't be visible when the home stack
is brought to the front to display the recents activity from an app.

- Also fixed issue with not setting correct return type for tasks
when they don't have Intent.FLAG_ACTIVITY_TASK_ON_HOME flag set.

Bug: 26571156
Change-Id: I45ef795c6a19ab859e9f6204fb059e875ad798c5